DIRECT ANALYSIS OF SOIL SUSPENSIONS BY INDUCTIVELY COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY FOR DETERMINATION OF TOTAL METALS

A rapid and efficient method is needed for determining total concentrations of multiple elements in soils. A procedure was developed whereby a soil was finely ground (25 min in a micronizing mill), suspended in water (2 g .cntdot. l-1), and analyzed directly by inductively coupled plasma-emission spectrometry (ICP) to determine total concentrations of Al, Ba, Ca, Fe, Mg, Mn and Sr. The average concentrations obtained for these elements in 10 soils agreed to within 2% of values obtained for the same oils analyzed after first solubilizing the samples by sodium carbonate fusion. The concentrations of the 7 elements determined in the 10 soils analyzed ranged from a low of 44 mg Sr .cntdot. kg-1 soil to over 7% of the soil samples as Al. The sensitivity of the direct analysis procedure could be increased by increasing the concentration of soil in suspension to 10 g .cntdot. l-1. Large variations in concentration due to particle size differences among soils were initially observed. Grinding the soil in a micronizing mill reduced the variation caused by the particle size differences. When 2 soils with sand compositions of 79 and 17% were ground for 25 min, particle size analysis showed that 81 and 90%, respectively, of the ground soil had a particle size of equivalent diameter < 2 .mu.M. The direct analysis of soil suspensions by ICP eliminates the time-consuming solubilization step required in other total analysis methods and allows for the simultaneous determination of the total concentration of multiple elements in soils.